“Color-plus-clear” coating systems involving the application of a colored pigmented basecoat to a substrate followed by application of a clear topcoat over the basecoat have become increasingly popular as original finishes for a number of consumer products including, for example, cars and floor coverings such as ceramic tiles and wood flooring. The base-plus-clear coating systems can have outstanding appearance properties, including gloss and distinctness of image.
“Tricoat” coating systems are used in certain coating applications. Such systems can achieve a deep transparent color effect as compared with the two-step base-plus-clear coating systems described above. Tricoat systems include an additional color-imparting non-hiding layer deposited between the basecoat layer and clear topcoat layer. A standard tricoat process involves the application of a first stage pigmented basecoat, with or without a reflective component, such as metallic and/or micaeous interference flakes, followed by the application of a second stage color-imparting non-hiding coating layer and then a clear topcoat.
One purpose of the color-imparting non-hiding coating layer in certain tricoat systems can be to provide color depth and richness to the basecoat layer, which is sometimes known as the “candied” effect. For example, in certain applications, an organic red non-hiding coating layer may be applied over a red metallic basecoat layer to enhance the red color depth and richness of the red metallic basecoat. In some tricoat systems, a color-imparting non-hiding coating layer provides a contrasting color effect over the basecoat layer because of the combination of colors applied. For example, in certain applications, an organic red non-hiding layer may be applied over a silver metallic basecoat layer to provide a red metallic appearance. In another example, an organic yellow non-hiding layer may be applied over a red metallic basecoat layer to provide an orange metallic appearance.
In some cases, such color-imparting non-hiding coating layers are applied over a basecoat layer as described above but without application of an additional clearcoat layer. In these instances, the color-imparting non-hiding coating layer typically provides properties similar to a traditional clearcoat.
In other cases, these color-imparting non-hiding coating layers may be applied as a single coating layer directly to a substrate with no basecoat or clearcoat layer present. Again, such color-imparting non-hiding coating layers typically provide both color and protection to the substrate.
Historically, dyes have been used to achieve a transparent coloration in such color-imparting non-hiding coating layers. In such applications, dyes are considered organic colorants that are completely soluble within the coating medium and which do not scatter light in the solvated state. Dyes, however, often possess poorer fastness than pigments when exposed to ambient light and weathering conditions. Dyes often possess poorer color persistencies than pigments due to their tendency to migrate to the surface of the coating. In certain dyes, heavy metals are incorporated to impart coloration and, in turn, enhance the fastness properties of the dyes. Many heavy metals, however, are considered toxic and, as a result, there are obvious health and safety concerns with their use. Additionally, dyes may migrate to the surface of the coating layer, which can lead to loss of color.
Thus, there is a need in the coatings art for coated articles having deposited thereon a color-imparting non-hiding coating layer that can have transparency and color comparable to that of a similar coating layer containing dyes and color persistence properties similar to conventionally pigmented coatings.